Evaluation of the effective focal spot size of x-ray tubes by utilizing the edge response analysis

Masayuki Nishiki

doi:10.1117/12.2081306

18 March 2015 Evaluation of the effective focal spot size of x-ray tubes by utilizing the edge response analysis

Masayuki Nishiki

Proceedings Volume 9412, Medical Imaging 2015: Physics of Medical Imaging; 94123Z (2015) https://doi.org/10.1117/12.2081306
Event: SPIE Medical Imaging, 2015, Orlando, Florida, United States

Abstract

Evaluation of the effective focal spot size of X-ray tube has been made utilizing the slit or the pin-hole camera, but is not widely used in a daily practice due to the need of specialized tools. The author proposes a simplified method in which only a metal edge and a digital detector are used, together with a process of removing detector blur inherently associated with the adoption of such a detector. The evaluation was made through the OTF (Optical Transfer Function) measurements by using the edge response analysis. Through the whole study, the use of OTF instead of MTF (Modulation Transfer Function) was essential in order to stay within the linear systems theory framework, at cost of handling complex functions. Evaluation steps were as follows; 1. The inherent OTF of the detector (OTF_det) was measured by acquiring an image of the edge being closely contacted to the detector. 2. The second OTF (OTF_multi) was measured with the edge placed apart from the detector so as to implement 2 times geometrical magnification of the edge. OTF_multi is the product of OTF_det and the focal spot OTF (OTF_focus). 3. OTF_focus was obtained by calculating OTF_multi / OTF_det, thus removing the detector blur completely. 4. The LSF of the focal spot was obtained through the inverse Fourier transform of OTF_focus. The resultant LSF_focus was assured to be a real function due to the fact that original LSF_det and LSF_multi were both real functions. Preliminary results well matched those obtained by the pinhole camera.

Citation Download Citation

Masayuki Nishiki "Evaluation of the effective focal spot size of x-ray tubes by utilizing the edge response analysis", Proc. SPIE 9412, Medical Imaging 2015: Physics of Medical Imaging, 94123Z (18 March 2015); https://doi.org/10.1117/12.2081306

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